Composting and the Decomposer Chart

Compost different waste materials and document their decomposition processes in class.


To learn why composting is important and how to do it


  • 2-liter plastic bottles cut in half (use bottom half)
  • Soil
  • Garbage
  • Chart
  • Writing utensil
  • Marker
  • Masking tape
  • Plastic wrap to cover the plastic bottles
  • Rubber bands
  • Composting Journal


45 minutes to begin, and then 5–10 minutes weekly for observations


This activity illustrates the different rates at which various substances decompose. The activity can lead to discussions about composting and solid waste disposal. 

Ask the kids to bring in a variety of different garbage items (food scraps, paper, plastic, wrappers, leaves, feathers, etc.). Fill each of the cut plastic bottles with 10 cm of soil, and set it on your windowsill. Put one or two pieces of trash in each bottle (depending on the size of the trash), on top of the soil. Add a little more soil on top, and moisten with water. With a marker, write on each bottle, perhaps on a piece of masking tape, the trash item it contains. Cover each bottle with plastic wrap held with a rubber band, and wait. 

Over the next several weeks/months, have the kids note what happens to the trash, keeping a record in a chart, such as the one below (Composting Journal). During every meeting, ask a kid to remove the cover to let each bottle get some air and to observe how each item has changed. Continue to add water and let the sun shine into your bottles. Otherwise, keep the lid closed for warmth and humidity. Make sure to ask the students for their responses to the changes. 

You can do this project for four weeks or longer. At the end of a month, imagine how long it will take plastic bottles and glass containers to disappear. Some items will remain longer than we do. Some items will disintegrate within a month. Note: If composting is occurring, this activity should not smell.

Composting Journal

Name of item: ___________________ Date: ______________

First noticeable change: __________________________________________________

When can you not recognize it? __________________________________________________

When does it disappear? __________________________________________________

Is it food or garbage? __________________________________________________

To follow up:

  • Discuss what will happen when we put plastic in the ground. What problems can this cause? What can we do to help solve this problem?
  • Discuss why composting is a preferable alternative to throwing trash away or burning it.
  • Have the kids share their results with parents and try composting at home.
  • Discuss what happens with leaves when they fall to the ground. Why don’t they pile up?

This lesson plan is an activity from the Environmental Activities for Youth Clubs and Camps, a resource developed by the Peace Corps Office of Overseas Programming and Training (OPATS). It was contributed by Peace Corps/Armenia.

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